stehlik



v Aug. 6, 1929. R, RSTEHLIK 1,723,087

AUTOMATIC TELEPHONE SYSTEM ori inal Filed Jan. 8, 1 27 a s s-sh et 1 \N om mrEn 01'* 1mm hFSIEhZik man- 1929- R. F. STEHLIK I 1,723,087

AUTOMATIC TELEPHONE SYSTEM Original Filed Jan. 8, 1927 2 Sheets-Sheet 2 -"IITUE TLZEF"- EudulphFETEhlik Patented Aug. 6, 1929.

UNITED STATES PATENT OFFICE.

RUDOLPH F. STEHLIK, OF CHICAGO, ILLINOIS, ASSIGNOR '10 RESERVE HOLDING COM- lPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF DELAWARE.

AUTOMATIC TELEPHONE SYSTEM.

Application filed January 8, 1927, Serial No. 159,813.

This invention relates in general to automatic telephone systems, but more particularly it relates to such systems in which line finders are employed to connect an idle trunk llue to a calling line; and the principal object of the invention, briefly stated, the production of a new and improved finder systenti, in. which primary line finders are directed to the contacts of a calling line, the in'iprovements being of such. a nature to permit a reduction in the cost ofmanu'it'acturing and maintaining oi said equipment without impairing its reliability or ellicicncy.

In one working embodiment of my invention, I employ directive finders of the one hundned point type, using switches similar to the well known Strowger connector, whose wipers are moved first in a vertical direction to select the desired level, and then in a horh zontal direction to select the desired contacts in that level. Switches oi this type have been used for this purpose heretofore, in which case it was necessary to employ several relays to control the functions of the switch.

' In the present invention I have simplified the switch mechanism, by excludingall re lays individual to it, thereby reducing the switch mechanism to its simplest form. In the simplified switch oi this invention I employ a back-acting release magnet, which functions as a switching relay when energized, serving to connect the wipers ot' the finders through to the trunk line outgoing from. it. Then the magnet deei'iergizes the switch mechanism is released-and allowed to return to its normal position.

The directive operations oil the finder switches of this invention are controlled through a common control n'lecl'ianism, which is associated with an idle finder through the medium of a finder allottcr.

its a further object of my invention I have simplified the control mechanism of a finder group, by reducing, the number of relays neccr-1sary and by combining the functions of the various switches in a manner which will be apparent hereinafter.

In the finder systems which have been used heretofore it has been possible for a connector switch to connect with the calling line after that line has initiated a call, and belore the finder switch has picked up the call. This results in the unnecessary operation of the finder switch, since when that switch arrives upon the cnntacts of the calling lino,

Renewed November 12, 1928.

it finds that line engaged and does not connect to it. In addition to the unnecessary operation of the finder switch, systems of this kind require a further complication in the finder switch mechanism itself, as that switch must be provided with circuit arrangements tor testing the busy or idle condition of the calling line after the wipers have been set upon it.

Accordingly, as a further object of my invention I provide circuit arrangements which mark the calling lines engaged in the cormector banks as soon as the calling sub scribers remove their receivers from the switch hook, even though the finder switch mechanism does not arrive upon the line until some time later.

It the calling line happens to be a line whose finder bank designation is a rather high number, such as 98 for example, and an appreciably long time elapses between the raising of the receiver and the connecting ot' the finder switch with that line. Notwithstanding that the subscribers of the system are instructed to wait for dial tone before beginning the manipulation of the calling device to set the switches for their call, many subscribers will have dialed a. digit or a part of a digit prior to the arrival of the finder upon the contacts of their line,

'with the result that their call lost because i the switches have not been in position to operate responsive to the manipulation of the calling device.

Accordingly a further object of my invention I provide a by-pass dialing circuit, tl'irough the medium of which the calling subscriber may operate his calling device immediately after he has removed his receiver, the switch train which he is to use being operated over this bypass dialing circuit prior to the establishment of the connection between the finder wipers and the contacts of the calling line. By this arrangement I am able to speed up the service given to the subscriber, since he hears dial tone immediately upon removing his receiver, and need not wait until. the finder switch has connccted with his line to begin the operation. of his calling device.

In a by-pass dialing system it is necessary to provide means to prevent the establisln merit of a bypass dialing circuit in case two or ii an subscribers initiate calls simulta- Aceowliugly as a. Further object of through to the trunk outgoingfrom it.

my invention I provide means operative in case of simultaneous calls, to prevent the establishment of the bypass dialing circuit, and further provide an arrangement for preventing the initiation of the second call during the interval required for the finder to connect with the first calling line and tor the finder allotterto select a second idle finder.

Further objects of my invention, not specifically mentioned here, will be apparent from the c etailed description and claims which follow.

Refer now to the drawings, comprising Figs. 1 and 2, which when arranged with Fig. 1 above Fig. 2 with the correspondin g1 y numbered lines in the line, show sutficient details oi my invention to enable a clear understanding of it. In Fig. 1, I show the calling stations A and B with theline equipment respectively individual to each. I show the finder switch which comprises a Strowger connector switch mechanism carrying wipers 65, 66, and 67 upon a shaft, not shown, which is operated first in a vertical direction and then in a rotary direction to position those wipers upon the contacts of a calling line. The finder switch F also contains a back-acting release magnet 5, which when energized closes the springs 51, 52, 53, and 54-, thosesprings serving to switch the wipers of the finder Release magnet 5 is maintained energized throughout the conversation, in which position it has established mechanical connections preparatory to releasing of the .switch mechanism to normal. The back-acting release magnet which I have employed in this finder switch is not new, the mechanical details of such an arrangement being shown in the patent 1,582,334: issued to IV. E. Campbell on April 27, 1926, the release mechanism and the method of attaching springs to the release armature being shown in detail in Fig. 4 of that patent.

In Fi 1 I also show theselector switch S, which is ofthe well known Strowger type, whose wipers are moved first in a vertical direction unoer the control of the callin device, and then rotated automatically in search of a calling line. A selector switch of this type is old and familiar to one skilled in the art, and need not be explained in detail at this time.

In Fig. 1, I also show a finder allotter, comprising wipers 7044, inclusive, and the magnet 7 6 which drives them. This finder allottor is mechanically of the type of the well known rotary lineswitch, whose wipers have no normal position and move in a forward direction only, being driven by the magnet 7 6- whose armature arrangement advances the wipers durin the deenergization of the magnet.

In Fig. 2, I show the control equipment which is common to the group of finders and associated with individual finders of that group to the finder allotter FA. of Fig. l. The control equipment comprises the vertical counting switch VCS, the rotary counting switch RCS, and the sequence switch SQ, which are each mechanically similar to the finder allotter FA referred to above. In the operation of the control device during the setting of t is wipers of the finder upon the contacts oi the calling line, the sequence switch SQ, vertical counting switch V03 and the rotary counting switch RCS are all set. Sequence switch SQ, makes one half of a revolution during the setting operation of the switch, at the end of which time it returns to normal under the control or a local circuit. The vertical counting switch VCS is stepped from its normal position a number of steps corresponding to the number of vertical impulses necessary to elevate the wipers of the finders opposite the bank level containing the contacts of the calling line. The counting switch VGS is then stopped, and remains in a position until the completion of the settingoperation, at which time it is returned to normal under the control of a local circuit. Similarly, the rotary counting switch, RC8, is stepped in synehronism with the rotary magnet, a number of steps corresponding to the number of contacts over which the wipers ot the finder must be moved to engage the contacts of the calling line. lVhen this number 01": steps has been taken the switch ROS is stopped, and remains stationary throughout the remainder of the switch setting operation, returning to normal at the end of that operation under the control of a local circuit.

Throughout the drawings I have shown a plurality of batteries, this being done to avoid unnecessary complications. In an installation ot the system of this invention, there would be but one battery, preferably with its positive. pole grounded.

While I have chosen to show my invention in connection with a certain type of apparatus I have done so by way of example only, as there are many modifications and adaptations which will be apparent to one skilled in the art, which can be made without departing from the scope of the invention.

in order to briefly explain the operation of the system of my invention, it will be assumed that the calling line A initiates a call. hen a subscriber thercat removes his receiver, the line relay 2 will be energized, and upon energizing, that relay establishes a locking circuit for itself which. maintains it energised independent of the calling subscribers loop. This locking circuit includes the right-hand winding of the line relay, and the relay 205 lot the control equipment.

switch. hen

Relay 205 is marginal, being so constructed that it will not energize in series with one line relay winding, however, in case there are two simultaneous calls, two line relays will be held energized through the winding of relay 205, in which case, that relay will. receive sufficient current to permit it to energize. The energization of the line relay also closes a circuit to the start relay, which pulls up and causes the control equipn'ient to deliver impulsr to the tinder magnet. As is the custom in directive finders of this type the line relay ii st marks the vertical designation of the calling; line in the banks of the vertical counting switch, so that the operation. of that switch will count oil the correct number of impulses to step the wipers up to the desired level. After the desired level. is reached, the vertical counting switch is stopped, the sequence switch continues to step, until it has passed its tenth bank contact. The vertical counting switch is prevented from operating by shunt circuit which maintains its magnet energized independent of the interrupter circuit over which it was initially operated. lVhen the sequence switch wipers have passed the tenth contact, this shunt circuit is broken, and the vertical counting SR. itch magnet falls back and advances the wiper one step, at which time the rotary designation of the calling line is marked in the banks of the rotary counting switch through contacts on the energized line relay. The impulses required to place the wipers on the contacts of the calling line are counted out by the rotary counting switch, which is now stepped in synchronisn'i with the sequence the correct contact is reached, a shunt circuit is provided for the motor magnet of the rotary countin' switch, maintaining that magnet energized independent of the irterriuptcr. The sequence switch continues to step until it has passed its twentieth bank contact, at which time the sequence. SWitCl'l goes into its switch through posi ion, the finder is switched through to the calling line, and the sequence switch stepped on to its home position. lVhen the sequence switch reaches its home position, a circuit for the motor magnet of the finder allr'rttcr is completed, and that allotter moves in search of another idle finder. When an idle finder is found, the guard relay, which was energized when the sequcnce'switrh reached its home position to start the operation of the lim'ler allottcr, is deenergized and the start circuit extended to the start the connection to the finder wiper. The calling subscriber operates the switches over the circuit which extends through his loop, through the control equipment, through the by-pass wipers of the iinder allotter, and thence through the upper winding of the line relay of the next switch to battery. This winding: is sufiiciently strong to energize the relay, and the subscriber will hear dial tone which is superiuqlosed upon battery supplied to that relay. The calling subscriber upon, hearing the dial tone manipulates his calling; device, to alternately open and close the circuit oi the line relay of the switch, which falls back and directs that switch in the well known manner. The establishment of the connection to the calling line contacts by the finder does not in any way interrupt the train 01 impulses which the calling subscriber may be direct ing at the time. IIaving thus described the operation or my invention in general, I will now proceed with a detailed description of this operation.

Line A initiates a col].

aisume new that the subscriber on line A desires to make a call, and removes his receiver ifrom the switch book. A circuit then completed from ground through springs 33, conductor. 88 through the calling telephone to conductor 87, tl'iro'ugh springs 34, spring 38 and ice break contact, through the left-hand winding of relay 2, through conductor 84k, through springs 212, through resistance 206 to battery. The line relay 2 energizes over this circuit and at sg irings el closes locking circuit for itself traceable from round through the righthand winding or the relay 2, springs 41, springs conductor through the windings of relay 205 to battery. Relay 205 being marginal, will not energir ie in serieswith the locking windingoil a single line relay, however the line relay 2 will be maintained in its energized position by the current flowing through the relay 205. The energization of relay 2 at springs 40, also closes a circuit from ground through conductor 89 to the private bank contact associated with the line A, in the banks of the connector switch. Ground on this private contact, marks the line engaged. and prevents the establishment of a coni'iection to it by a com'iector. The enewization oi' line relay 2, at springs 35 marks the vertical designation of the calling line in the banks of the vertical countii'ig switch VCS, for a purpose which will be explainedv in detail hereinafter. At springs 36, the line relay, prepares a rotary mark.- inp; circuit which will. also be explained in detail. hereinafter. 37, closes a circuit to ground the start conductor, energizing); the start relay 203 over circuit traceable from ground through Line relay 2, at springs,

springs 37, conductor 83, through springs 221, through the winding of the start relay 203 to battery. The start relay energizes, and operates springs 213216, inclusive, to arrange the control equipment so that it will deliverimpulses to the magnets of the finder switch, to direct the wipers of that switch to the contacts of the calling line. The energization of start relay 203, operates springs 212, which opens the battery connection from the remaining line relays of the group, to prevent the energization of any of those line relays during the interval that the control equipment is engaged.

The by-pass dialing circuit.

As soon as the line relay 2 has energized and locked itself, the calling subscriber will hear the dial tone, over circuit traceable from battery through the secondary winding of the dial tone transformer 18, through the upper winding of relay 8, springs 58, trunk conductor 101, through the bank contact and wiper 7 1 of the finder allotter, conductor 109, springs 213, spring 220 and its break contact, conductor 86, through spring 38 and its make Contact, springs 34, conductor 87 and thence through the receiver of the calling telephone A, conductor 88, springs 33 to ground. The line relay 8 of the selector S energizes over this circuit, and prepares the selector for the reception of impulses in the usual and well known manner. The calling subscriber upon hearing the dial tone, is informed that the equipment is in. readiness for the reception of the directive impulses, and operates his calling device in accordance with the first digit of the called number. The calling device interrupts the circuit just traced for line relay 8 of the selector, causing that relay to fall back and close the circuit traceable from ground to spring 01, springs 55, springs 57, relay 10, to the vertical magnet 56, energizing that magnet to elevate the shaft of the wipers of the selector one step. This selector opera tion is standard and well known, being described in chapter 5, on page 21, of the book Principles of Automatic Telephony by Harry P. Mahoney. The operation of this switch being well known, will not be repeated here, it being sufficient to state that after the vertical operation of the switch, it is rotated to select an idle trunk, and the relay 12 is operated to extend the trunk conductors 101, 102, and 103 to the wipers 62, 68, and 6 t through springs 58, 59, and 60. If the finder has not established a connection with the contact of thecalling line prior tothe operation of relay 12 the line relay of the next switch, which is similar to the line relay 8 of the selector S, is energized over its upper winding, and operated in the manner just set forth for the line relay 8. In all probabilities,however, i/l18'.'fi11d5r,,F will; 68

tablish a connection with the calling line sometime during the operation of the vertical magnet, and the remaining switches of the train will be operated orer the usua loop circuit, which is traceable from wiper G2 to springs 58, trunk 101, springs 51, which will be operated when the release magnet 5 is energized during the switch-through operation of F as will be set forth hereinafter, wiper 65, contact 27, line conductor 87, through the calling telephone, the line con ductor 88, contact 29, wiper 67, springs 5st, trunk conductor 103, springs 60, to the wiper Impulsiag the finder.

Returning now to the energization of the line relay 2, it will be noted that the line A terminates in the twenty-third set of contacts in the finder bank, consequently it will be necessary for the finder F to take two vertical steps to reach the second level, and to be rotated through three rotary steps to reach the third set of contacts in that level, that is, the contacts of the line 23. Accordingly, when the line relay 2 is energized, spring 35 upon placing ground upon conductor 80, places the ground on the second bank contact of the counting switch VCS, over which the wiper 208-rotates. The energization of the start relay 203, at spring 215 and its make contact, places ground onthe conductor 113, thereby closing a circuit from that conductor through interrupter 225, through the winding of the magnet 224 of, the sequence switch SQto battery. Magnet 22% energizes during the time that the interrupter 225 closes the above traced circuit, and deenergizes when that interrupter opens that circuit. Mechanically the sequence switch SQ, is like the well known rotary lineswitch, whose wipers are advanced during the deenergization of the magnet 224. Simultaneously with the establishment of the circuit toithe magnet 224, a circuit is established from ground through springs 217, through the interrupter 226, conductor 114, wiper 221, thence over two paths in parallel, the one leading through conductor 116,

through springs 216, through the winding 7 ofthe magnet 202, of the vertical counting switchVCS, to battery. The second parallel path leads over the conductor 106, through the wiper 72 of the finder allotter FA, thence through the vertical magnet 6 of the finder F. These magnets are energized and deenergized by the alternate closing and opening of the above circuit by the interrupter 226. The interrupter's 225 and 226 are geared to the same shaft, and arranged to close their respective circuits simultaneously. The vertical counting switch magnet upon energizing, prepares to ad Vance thewipers 20S-21,0, inclusive, of th switch one step, the actual: advance with the grounded number 1 contact of its bank. A circuitmay then be traced troin ground through springs 35, conductor 80, second bank contact and wiper 208 of the counting switch VCS, conductor 227, through the multiple of contacts 110 and wiper 220 of the sequence switch SQ, conductor 114C, viper 221 and its bank contact multiple 1-10, thence over the previously traced parallel paths to the vertical magnet (3, and the magnet 202 of the counting switch VCS. It will be noted that this circuit maintains those magnets energized in- (lCPGTltlGBt ot the interrupter 22G. Interrupter 225 is not however short circuited, and the sequence switch is advanced step by step by means of that interrupter. When the WlpOlS 220 to 2223, inclusive, have passed oi? their respective bank contacts No. 10, the above locking circuits of magnets 202 and are open, and these fall back, the latter witnout any particular" eitect, and t is torn er to advance the wipers 208 to 210, inclusive, an additional step into engage ment with the third contact set of the bank. i i hen sequence switch wiper 221 moves into engagement with its eleventh bani; Contact, the circuit through interrupter 226 and conductor 11 i .is extended through conductor 10'? thence over parallel paths, the one through conductor 111, springs 21 i, thence through. the winding of the magnet 201 oi the rotary counting switch RCS, to battery, and the second parallel circuit is extended over conductor 107, through wiper 73 oi: the finder allotter FA, through the winding of the rotary magnet 7 of the finder F, to bat tery. This arrangement causes the rotary nurgnct 7 and the motor magnet 201 ot the ri'il'ary counting switch RCS to he stepped in s nu-hronism with the sequence switch SQ. Since the calling line is No. 23 in the tinder hank, three rotary steps must be taken. At the end of the second impulse, when the rotary counting switch RC8 advances its wipers onto the third bank contact, circuit may be traced from ground on wiper 209. through the third bank contact engaged by that wiper, conductor 81, through springs 36, conductor 82, through the third hank contact and wiper 207 of the you! rotary counting switch ROS, conductor 112, through the contact multiple 1120 and the wiper 220 of the. sequence switch SQ, conductor 1141, wiper 221 and its bank contact multiple 1120, conductor conductor 111, springs 21 1, through the winding of the magnet- 201 to battery. This circuit also extends over conductor 107 through wipers 78, through rotary magnet 7 to battery. The rotary magnet is energized and maintained energized over this circuit, to advance the wipers on additional step to bring them into engagement with the contacts of line h lagnet 201 is energized and maintained energized independent of the interrupter 226, to prevent further stepping oi the switch ROS at this time. The sequence switch as before continues to step, the locking circuit being maintained until the wi ers 220 and 221 leave their respective bank contacts No. 20.

The finder is switched through The sequence switch magnet 22 i is alternately energized and deenergized by the operation of interrupter 225, to advance the Wipers step by step towards their home position. \Vhen wiper 221 engages its bank contact 21, and the interrupter springs 226 close, a circuit may be traced from grounded conductor 11 1, wiper 221, conductor 105, through wiper 71 of the finder allotter, through the winding of the release magnet 5 of the tinder F, to battery. Release magnet 5 energizes and closes springs 51 and 541 to extend the calling line to the trunk conductors 101 and 103, respectively and to extend the release trunk conductor 102 through springs 52. Relay 5 upon energizing stablishes a locking circuit for itself traceable from grounded release trunk conductor 102 through springs 52, resislance 13, springs53, through the winding of the magnet 5 to battery. The operation of springs 52 extends the release trunk ground conductor down to the bank contacts of the finder allotter, over which the wiper rotates, for

purposes which will be hereinafter explained.

The extension of release trunk 102 through springs a2 and wiper 66, now engaging contact 28, completes the circuit of cut-oil relay 1, traceable from that grounded contact through the winding of the relay 1 to battery. Relay 1 energizes over this circuit, opening springs 39 to break the locking circuit of relay 2, and opening springs 33 and 341, to open the bypass dialing circuit and to clear the calling line of attachments. The line relay 2 restores immediately, connecting the release trunk to the private normal 89, so that the line A is maintained busy to the connectors by the release trunk groitmd, as is customary in automatic telephone systems. Thus itwill be seen that I have provided the usual trunk loop from the calling line through the line equipment and finder without attachments so that dialing and conversation may be accomplished under the same conditions as used heretoior.

F lmlcr allotter aml other idle finders.

As the sequence switch, continues in its step-by-step travel towards its home position, wiper 223 encounters its bank contact 24, at which time circuit for the magnet 76 of the finder allotter and the guard relay 204 is established, that circuit being traceable frem ground picked up by wiper ot the finder allotter through conductor 104, wiper 223, bank contact 24, conductor 108, conductor 108 through the relay 204 to battery, the circuit also extends over conductor 108, through interrupter spring 7 5, magnet 76 of the finder allotter to battery. Relay 204 energizes, and magnet 7 6 energizes. Magnet 76 upon energizing prepares to advance the wipers 70 to 7 4, inclusive, one step, and at interrupter spring opens its own circuit, permitting the magnet to deene'rgize, and advance the Wipers. If the next finder of the group happens to be busy, wiper 70 picks up another grounded contact, again closing a circuit over conductor 104, to maintain guard relay 204 energized, and to reestablish the circuit for the motor magnet 76. As long as the wiper 70 encounters grounded contacts, the magnet 76 will be energized. and the buzzer-like action will continue to rotate the wipers in search of an idle finder. l/Vhen the idle finder is encountered, the magnet becomes dcenergized, the circuit of guard relay 204 no longer completed that relay restores to normal. That relay 204, upon energizing opens the circuit to the start relay 203, to permit that relay to fall back preparatory to advancing the counting switches into theirnormal position. Relay 204 in its energized position, prevents the reenergization of start relay 203 prior to the allotting of an idle finder by'the finder allotter FA.

Control equip meal returns to normal.

When the start relay 203 deenergizes, it opens at springs 2 15 the circuit over which the sequence switch and counting switches were impulsedand at the same springs closes the circuit to conductor 115. The deenergi'zationof relay 203 also closes springs 218 to complete the restoring circuits. The sequence switch is restored over a circuit traceable from ground through springs 218, conductor 117, wiper 222 and the multipled bank contacts it engages, conductor 115, spring 215 and its break contact, interrupter 225, magnet 224 to battery. The magnet 224- is pulsed over this circuit by the operation of interrupter 225, to move the wipers 220-22301? SQ, to their normal position, at which time wiper 222 engages contact 1. Since contact 1 is not connected with the other contacts in the multiple, the circuit just traced for magnet 224 is broken, and the sequence switch remains in its normal position.

-Magnet 201 of the rotary counting switch is also energized by the deencrgization. of relay 203 over a circuit traceable from ground through spring 218 and its break contact, conductor 115, wiper 206 and its bank contacts all of which are multipled together except the No. 1 contact, inter-- rupter springs 209, through the winding of the magnet 201 to battery. The magnet upon energizing interrupts its own circuit at springs 209 and operates in a buzzer-like fashion to advance the wipers 206 and 207 into engagement with the bank contact No. l, which is not connected with the multiple of the remaining of the contacts, and there fore the circuit of magnet 201 is not again completed. At the same time grounding of conductor 115 closes a circuit through wiper 210 and the multiple contacts of its bank, through the interrupter springs 219, through the winding of magnet 202 to battery, that magnet energizing preparatory to advancing the wipers 208-210, inclusive, of the vertical counting switch VCS, and interrupting its own circuit at interrupter springs 219. Magnet 202 therefore operates in a buzzer-like manner until the wiper 210 is in engagement with. the number 1 ban contact, which is not multipled to the remain ing contacts of the bank. The control equipment is new in its normal position, when the finder allotter finds an idle finder, and relay 204 deenergizes, the start wire circuit is extended to the start relay and the equipment is in readiness for the next call.

Simultaneous calls.

Assume that immediately after line A has initiated a call, and line relay 2 has been. energized, a second line tries to initiate a call. The energization of start relay 203', responsive to the energization of the line relay 2, removes the battery from the conductor 84 at springs 212, thereby removing battery from the leiithand winding oi the remaining line relays of the group, preventing any of these line relays from energizing. The calling subscribers do not hear the dial tone and they do nothing until. finder equipment becomes idle and permits their 1 ie relays to energize preparatory to starting the call. It is necessary in this system to remove battery from the line relay to prevent that relay from energizing, since the icy-pass dialing circuit is established, and the finder once started, it is imperative that it connect with the calling line which started it, rather than to some other calling line whose finder bank designation happens to be lower, as would be the case if the line relays of all calling lines were operated immediately.

Assume now that two lines A and B initiate calls absolutely simultaneously, and that their respective line relays 2 and 4: are both energized, and lock themselves through their respective right-hand windings through springs 4. .1 and 49, 30 and 50, through conductor 85, through the winding of marginal relay 205 to battery. When two locking windings of the line relays are connected to conductor 85, suilicient current lows through the winding of the marginal relay 20:") to permit that relay to energize. The energization of relay 205, closes springs 220, closing a circuit from. ground tl'lrough those springs, springs 213, conductor 109, through the by-pass wiper T l oil? the finder allotter, trunk coiu'luctor 101, springs 58 of the selector S, through the upper winding of the line 8 to battery. The line relay 8 is energized, and closes at springs circuit for the release relay 9, which energizes and at springs 50 applies ground to the release trunk conductor 102. The by-pass dialing circiilit is not completed, being held open by spring 220 and its break contact of the relay 205. Obviously since two lines are in calling position, both of them cannot control the selcc tor S, and the by-pass dialing circuit of no utility. The calling subscriber does not hear the dial tone then until the finder F switches through, which it readily does and locks itself to release trunk 102, which has been grounded by the release relay 56 of the selector as explained above. In case of the two simultaneous calls A and B, the line having the lower finder bank designation, will be served first, that is the line A whose number is 23 in the finder banks. As soon as the control equipment has completed its cycle of operation. incidental to the setting oil? tl e finders upon the bank contacts 23, and restored itself to normal, the line B is served. The operation of the cut-oil relay 1 opens the winding of the line relay 2 from the conductor 85, iowever, the decrease in current cause by this operation is not sufiicient to cause the relay 205 to fall back, that relay remaining in its energized position, so that the calling subscriber on the line B does not hear the dial tone until the finder F has connected with that line.

Release of the selector 8 finder F and Zinc equipment.

The calling subscriber manipulating the calling device at his station in accordance with the directory number of the wanted party, establishes a connection to that line through a switch train containing a number of switches depending upon the number of digits in the system. During the entire switch setting and conversational periods,

the release trunk conductor 102 is maintained grounded by the release relays of the various switches employed through springs similar to the springs 56, in the selector S,

as is explained in detail in the above reference. Switching relay 12 of the selector is maintained in. its energized position from the ground on its release trimlr. conductor 102. In the finder, release magnet 5 is maintained. energized from the ground on con.- ductor 102 through the resistance 1?) and springs 53, and the line equipment cut-oil relay 1 is maintained energized from the ground on conductor 102, through wiper 66, contact 28, and the winding of the relay to battery. hen, the convers tion is finished and the subscribers have replaced their receivers, the release trunk ground is taken. oilt', permitting the relay 12 to deenergize, permitting the release magnet 5 to demiergize, and permitting the cut-oil relay 1 to deenergicce. The deenergization of the switching relay .12 completes the release circuit and the selector S is restored to normal in the well known manner. The deenergization of the release magnet 5 opens the spring 51 54, inclusive, and also withdraws the retaining pawls from the switch shaft, permitting the shaft to fall to normal. in a manner identical to that explained in the above mentioned patent. Restoration ofcuhotl relay 1 restores the line circuit of line A to normal in readiness for the next call.

Having thus described my invention, what I consider new and desire to have protected by Letters Patent is pointed out in the appended claims.

lVhat is claimed is:

1. In a telephone system, a finder switch and a selective switch directly connected together, a line terminating in the banks of said. finder switch, a line relay associated with and individual to said line, means res sponsive to the initiation of a call on said line for operating said line relay to start said finder to establish a connection between said line and said selective switch, and means controlled by said line relay for extending said line over a bypass circuit to said selective switch over which circuit said selective switch is controlled prior to the establishment of said connection by said finder.

2. In a telephone system, a trunk link comprising a finder switch and a selective switch, a line circuit, means controlled over said circuit responsive to the initiation oil: a call for starting said finder switch to estalr lish a connection to said line circuit, and means operated by said first means to immediately establish a temporary connection between said line circuit and selective switch over which said line circuit may control said selective switch prior to the establish ment of said connection by said finder.

3. In a telephone system, a trunk link operated by said comprising a finder switch and a selective switch, a line circuit, means controlled over said circuit responsive to the initiation of a cal for starting said finder switch to establish a connection to said line circuit, means first means to immediately establish a temporary connection between said line circuit and selective switch over which said line circuit may control said selective switch, and means operated after said finder has connected with said line circuit to connect said finder and selective switch together and to destroy said temporary connection without interfering with the control of said selective switch by said line circuit.

, i. In a telephone system, a group of subscribers lines, a finder switch having access to said lines, a selective switch associated with said finder, a dial tone source associated with said selective switch, means responsive to a call on one of said lines to render said finder and selective switches in the exclusive use of said line, and to said finder to establish a connection to said line, means responsive to said first means to establish a by pass circuit to said selective switch, over which by pass the dial tone is audible to the calling line and over which said selective switch may be controlled prior to the establishment of said connection by said fine or.

5. In a telephone system, a line, a finder switch having access thereto, control equipment including means for directively operating said finder to establish a connection with said line, impulsing and impulse counting devices in said control equipment, means on said line operative when that line is calling to register its numbers in said counting device, and to start said impulsing device, a sequence switch in said equipment, primary, secondary and switch thru magnets in said findeig'a wiper on said sequence switch, contacts successively engaged by said wiper, the first group of said contacts lead: ing to said primary magnet, the second to said secondary magnetand the third to said switch thru magnet, means for stepping said sequence switch wipers over said contact groups to direct the impulses from said impulsing device to said respective magnets, and means cooperating with said wiper to govern the number oi impulses deliv red to each magnet in accordance with the numbers registered.

contacts in said sequence switch banks, the number of contacts 01 each group corresponding to the maximum number of impulses that can be sent to the respective switch magnets, means for registering a number in said counting switch, circuit means over which the first of said interruptcrs operates said counting switch and primary magnet in multiple and over which said second interrupter operates said sequence switch, and means operable when said counting switch has counted the registered number to short circuit said first interrupter mechanism until said sequence switch has passed over the corresponding commoned contact group.

7. In a telephone system, a finder switch having a release magnet, and a shaft, a release mechanism operative to release said shaft when said release magnet deenergizes, a soring set, a trunk line, wipers on said switch, and means including said spring set for energizing and maintaining said'release magnet to connect said wipers to said trunk.

8. In a telephone system, a line terminating in two sets of terminal contacts and in a relay set individual to it, battery potential normally maintained on the guarding terminals of said sets, a pair of switches having accessto said terminals, one of said switches extending calls from said line and the other extending calls to it, means responsive to the initiation of a call on said line for applying ground potential to only a certain one of said guarding terminals to prevent the establishment of a connection therewith by said latter switch while the other guarding terminal is unaltered.

9. In a telephone system, a link circuit comprising a finder and a selector, a line accessible to said finder, a relay associated with said line energized in response to the initiation of a call, means for locking said relay in its energized position, means controlled by said relay for starting said finder to establish a connection with said line, and

means also controlled by said relay for ex tenchng sa1d line to said selector independent of said finder.

10, In a telephone system, a link circuit comprising a finder and a selector, a plurality 01'? lines accessible to said finder, a line relay associated with each of said lines, energized in response to the initiation of a call on that line, a marginal relay common to saidlines, means for locking said line relays energized in series with said marginal relay, said marginal relay energizing only if two or more line relays are locked through it simultaneously, means controlled by said line relays for extending a by pass circuit toward said selector independent of said finder and means controlled by said marginal relay in its energized position for preventing the completion of said by pass circuit.

11. In a telephone system, a link circuit comprising a finder and a selector, a plurality of lines accessible to said finder, a line relay associated with each of said lines, energized in response to the initiation of a call on that line, means for locking said line relays in their energized positions, means establishing a circuit from an energized line relay to said selector independent of said finder and means for preventing the establishment of said circuit if two or more line relays are locked energized simultaneously.

12. In a telephone system, a line terminating in two sets of terminals one set for calls outgoing from said line and the other set for calls incoming to it, a guard terminal in each of said sets, connections between said terminals for maintaining them at a certain. potential to mark said line idle, and means responsive to the initiation of a call on said line for altering the potential on the incoming guard terminal to mark the line engaged to incoming calls without altering the potential on'the outgoing guard terminal.

13. In a telephone system, a line terminating in two sets of terminals one set for calls outgoing from said line and the other set for calls incoming to it, a guard terminal in each of said sets, connections between said terminals for maintaining them at a certain potential to mark said line idle, a line relay associated with said line and energized responsive to the initiation of a call on said line, and means responsive to the energization of said line relay for breaking the connection between said guard terminals and for altering the potential on the incoming guard terminal without altering the potential on the outgoing guard terminal to render the line busy to the incoming terminals.

14. In. a telephone system, a group of subscribers lines, a finder switch having access to said lines, a selective switch associated with said finder switch, a dial tone source associated with said selective switch, means responsive to the initiation of a call on one of said lines for making said tone immediately audible to said line, and means for starting said finder to establish a connection with said line.

15. In a telephone system, a group of subscribers lines, a finder switch having access to said lines, a selective switch associated with said finder switch, a dial tone source associated with said selective switch, means responsive to the initiation of a call on one of said lines for making said tone immediately audible to said line and for starting said finder to establish a connection with said line, and means responsive to the establishment of said connection for disabling said first means and for making said tone audible to said line over said connection.

16. In a telephone system, a trunk link comprising a finder switch and a selective switch, a line circuit, a start relay for in itiating the operation of said finder, means controlled over said circuit responsive to the initiation of a call for energizing said start relay to start said finder to establish a connection to said line circuit, and means operated by said start relay to immediately establish a temporary connection between said line circuit and selective switch over which said line circuit may control said selective switch prior to the establishment of said connection by said finder.

17. In a telephone system, a trunk link comprising a finder switch and a selective switch, a line circuit, a dial tone source associated 'ith said selective switch, means responsive to the initiation of a call over said line circuit for starting said finder switch to establish a connection, and means for immediately establishing a temporary connection between said line circuit and said selective switch over which said tone is immediately audible in said line circuit and over which said line circuit may control said selective switch prior to the establishment of said connection by said finder.

In witness whereof, I hereunto subscribe my name this 4th day of January,

RUDOLPH F. STEHLIK. 

